This invention is a continuation-in-part of my copending U.S. patent application Ser. No. 917,487 filed Oct. 10, 1986 under the title METHOD AND APPARATUS FOR TESTING OPTICAL COMPONENTS, now abandoned.
1. Field of the Invention
The subject matter of this invention is optics, and relates more particularly to an optical method and apparatus for scanning and testing the quality of refractive and reflective optical components.
The standard technique for testing the quality of optical components is interferometry. The fundamental limits of sensitivity of this method are determined by "shot noise" in the light beam over the area being tested, and by the quality of the optical components of the interferometer.
The current standard instrument used in industry for testing of optical components is the Twyman-Green interferometer. This device has certain inherent limitations. To begin with, it produces a fringe pattern from which it is difficult to extract quantitative information. Second, the fringe pattern has proven to be quite sensitive to vibration of the interferometer. Finally, its sensitivity is limited to approximately one one-hundredth of a fringe.
2. Description of the Related Art
British Patent No. 894,953 to Schafer et al, published Apr. 26, 1962, is the most relevent prior art we know of. Schafer et al discloses an optical surface test apparatus in which a test surface is scanned, one line at a time, by a laser beam. The incident laser beam is directed at a two-surface reflector, or roof reflector, which redirects the incident beam onto the test surface. The roof reflector is moved in one direction along an X axis, causing the incident laser beam to scan a single line on the test surface. At the end of each scan, the test surface is displaced a small amount in the Y direction, whereupon the incident beam is then scanned again in the X direction. In short, the light beam is scanned back and forth, and the test object is incrementally displaced at the end of each line scan.